Update all Mastodon product screenshots to 4.3
Updates all screenshots for Using Mastodon section to 4.3 style.
I may leave this for a couple of days before merging while other 4.3 pieces come into place.
I'm wondering if this should be merged as-is or if this would instead be the appropriate time to introduce versioned docs...
The existing screenshots are from 3.0 in many cases. Even if we had multiple versions they wouldn't be these.
I'm saying that the versions would be 3.x and 4.x
There aren't any supported versions of 3.x.
We should probably merge this for the release today?